Here is the text for Amos 9 in Greek and English. The quote in Acts 15:17 is a paraphrase of the Greek text.You weren't specific, but if you referring to the verse actually quoted from Amos, 9:11, I don't see a substantive difference. If you are referring to the context in which it was used, provided, by Acts 15::17, then there is no verifiable evidence for your claim. In other words, without a copy of Amos which predates Acts there is no way to tell if the translation, the LXX, was revised to match Acts 15:17.
It is agreed that Acts 15 is an accurate record of what occurred, but there is no evidence to support your claim that Acts 15:17 quotes Amos 9:12 from the LXX rather than Amos in the LXX being revised to match Acts 15:17.